Intra-arterial devices used to assist in the management of critically ill patients with cardiopulmonary failure have become commonplace at most advanced medical centers in the past decade. Extracorporeal membrane oxygenation (ECMO) and intra-aortic balloon pumps (IABP) are two of the most commonly utilized percutaneous strategies. Temporary use of inotropic medications and IABP is successful in weaning the majority of patients from cardiopulmonary support; however, a small fraction are refractory. Similarly, only a small minority of patients with acute respiratory distress syndrome (ARDS) will not respond favorably to conventional treatment modalities (mechanical ventilation, permissive hypercapnia, positional maneuvers) and will need to go on to increased cardiopulmonary support provided by ECMO. Because these devices are often inserted from a transfemoral approach, understanding the indications, techniques, and complications that can arise from use of these devices is important for the vascular surgeon who is often called upon to manage the immediate and long-term problems that arise.
Intra-Aortic Balloon Pump
The IABP, developed as 15-French in the 1960s, is a polyethylene balloon mounted on the end of a flexible 7–9-French catheter. It is typically inserted in a percutaneous fashion via the common femoral artery or the brachial artery utilizing the Seldinger technique. In unusual circumstances where femoral or brachial access is prohibitive, such as iliac artery occlusion, upper extremity dialysis access, or occluded axillosubclavian arteries, the IABP may need to be placed via the subclavian or axillary arteries. This approach typically requires cut-down with direct arterial puncture or in some cases, the anastomosis of a short 6–8-cm prosthetic graft. IABPs can be inserted through supra-inguinal bypass grafts percutaneously or via cut-down. LaMuraglia and colleagues evaluated 19 IABPs inserted through supra-inguinal prosthetic bypass grafts and found no significant increase in complications. Two patients in the analysis did require thrombectomy of occluded graft limbs and one developed a graft infection. Careful wound care and limiting catheter dwell time can help minimize risk of graft infection and bacteremia in IABPs placed through prosthetic grafts or native arteries.
The IABP is positioned in the descending thoracic aorta between the second and third intercostal space ( Fig. 42.1 ). The balloon should be positioned in the suprarenal aorta in order to provide 85%–90% occlusion with pulsation. At the start of diastole, the balloon inflates, augmenting coronary perfusion. At the beginning of systole, the balloon deflates and blood is ejected from the left ventricle, thereby increasing cardiac output and decreasing left ventricular stroke work and myocardial oxygen requirements.
Approximately 70,000 IABPs are inserted in the United States alone representing 5%–10% of all patients undergoing cardiac surgery. Complications secondary to IABP are high and reported on average in 20%–30% of cases. Thrombocytopenia is currently the most common complication noted in 50% of patients followed by fever in 40% of cases. Bleeding, along with aorto-iliac artery injury, dissection, thromboembolism, distal lower extremity ischemia, and balloon rupture occur less frequently.
Thrombocytopenia results from mechanical injury from the balloon to the platelets rendering them dysfunctional. Patients are typically anticoagulated systemically with unfractionated heparin during use of IABP. Thrombocytopenia in the face of full anticoagulation may precipitate spontaneous bleeding at remote sites other than the point of access. Administration of platelets, along with decreasing the level of systemic anticoagulation, can help reverse bleeding. If bleeding is significant and persistent, anticoagulation may need to be temporarily suspended.
Access site complications from IABP insertion may result in distal limb ischemia if the caliber of the brachial or femoral artery is inadequate to allow arterial flow around the sheath. Systemic anticoagulation and collateral flow around the sheath may help mitigate severe ischemia until the IABP can be removed. Arterial duplex imaging distal to the access site can be reassuring in documenting adequate distal perfusion. If profound ischemia persists, then moving access to a different site may be necessary for limb preservation. If the access is relocated, vigilance should still be maintained for possible compartment syndrome in the initial limb because of relative ischemia/reperfusion. In cases where access relocation is not possible secondary to the patient’s underlying condition, a life over limb posture may be necessary. Alternately, an antegrade access to the SFA can be performed at the time of IABP insertion or if limb ischemia develops. This antegrade sheath is then connected to the pump, diverting some flow distal to the occluding catheter.
The positioning of the IABP in the descending thoracic aorta is critical for proper functioning. The balloon size is chosen by the patient’s height and possible aortic diameter. By design, the IABP should provide 80%–90% aortic occlusion. Overestimating the size of the descending thoracic aorta may result in aortic dissection or rupture. Although known descending thoracic aortic dissections or aneurysms are contra-indications to IABP placement, at times the balloon may have been placed in an area with atheromatous plaque. Ongoing IABP counterpulsations may lift the plaque resulting in possible atheromatous embolization or intraplaque hemorrhage and possible dissection of the aorta. Direct aortic injury can be disastrous particularly if acute intervention is necessary and the patient is unable to tolerate removal of the IABP. If the patient is stable, balloon removal can be undertaken and the aorta treated as indicated. Focal aortic injuries can be treated with endovascular means such as aortic cuffs or stent grafts if the patient is stable. Embolization can occur to the brain, spine, mesenterics, renals, or peripheral circulation and may not present itself immediately.
Occasionally the balloon may migrate or be inadvertently positioned too high or too low in the descending thoracic aorta. This can result from vessel tortuosity, overestimation, or underestimation of the patient’s height and aortic size, which may give rise to malpositioning. More often than not, the IABP is put in as an emergency procedure without full knowledge of aortic caliber. Arch aortography performed at the time of balloon placement should identify the left common carotid and subclavian artery origins but will not always give an accurate estimation of aortic diameter. If the IABP is placed too high, there may be occlusion of the left subclavian or carotid arteries resulting in possible cerebral ischemia, stroke, or decreased upper extremity perfusion. Migration secondary to vessel tortuosity or positioning the IABP too low may result in malperfusion to the mesenteric and renal arteries. In both cases, the IABP will need to be repositioned appropriately and in some cases a new balloon sterilely inserted.
Extracorporeal Membrane Oxygenation
Mechanical cardiopulmonary support is typically thought to be a technique utilized during cardiac surgery; however, it can be utilized in a more prolonged fashion outside of the operating room. This is referred to as extracorporeal membrane oxygenation (ECMO) and is used in conditions such as heart support after cardiac failure, pneumonia, trauma, or severe infection. ECMO has existed since the 1970s and was used primarily in severe neonatal respiratory failure. Earlier trials in adults were unsuccessful, however, because technology and protocols improved and so did outcomes. ECMO utilization has risen in the last decade in part because of the publication of the CESAR ( C onventional versus E CMO for S evere A dult R espiratory Failure) trial in 2006, which revealed ECMO to be more effective than conventional ventilation therapy. Two types of ECMO exist to provide respiratory support: venovenous (VV) and veno-arterial (VA). Only VA ECMO provides hemodynamic support in addition to respiratory support. VA ECMO has increased in popularity over the past four decades. It has been used for various cardiac diseases complicated by cardiac failure including postcardiotomy syndrome after pericardiotomy, fulminant myocarditis, acute coronary syndrome, or as a bridge to mechanical circulatory support or transplant.
The ECMO vessels cannulated depends upon the underlying clinical need. Traditional VV ECMO typically involves femoral and internal jugular vein cannulation and utilizes cannulas between 20 and 24-French. VA ECMO utilizes femoral vein and femoral artery access ( Fig. 42.2 ). Stroke, renal failure, and sepsis (not infrequent complications seen in critically ill patients) are among the most common complications. The most frequently reported complication of VA ECMO was major hemorrhage, which led to reintervention in nearly half of patients, even in good quality studies. The insult of the initial operation, systemic heparin, and heparin-coated circuits are the typical causes of bleeding and managed in the usual way.